In one aspect, this invention pertains to an olefin metathesis process wherein an α-functionalized internal olefin, such as methyl 9-octadecenoate (methyl oleate), is converted in two metathesis steps to an α,ω-functionalized olefin, such as methyl 9-decenoate, and a co-product α-olefin, such as 1-decene.
“Metathesis” generally refers to a chemical process wherein two reactant olefins, either identical or different in composition, react through double bond (C═C) scission and reforming to form one or more product olefins that are different from the reactant olefins. When the reactant olefins are identical in composition, the process is a “homo-metathesis.” When the reactant olefins are different compositions, the process is a “cross-metathesis.”
Cross-metathesis of α-functionalized internal olefins, such as unsaturated fatty acids or unsaturated fatty acid esters, with ethylene produces valuable α,ω-functionalized olefins and α-olefins as products, typically characterized by chain lengths intermediate between the chain lengths of the reactant olefins. As an example, methyl 9-octadecenoate (methyl oleate) can be metathesized with ethylene in the presence of a metathesis catalyst to prepare methyl 9-decenoate and 1-decene. α-Olefins, such as 1-decene, find utility in the manufacture of poly(olefin) polymers. α,ω-Unsaturated esters, such as methyl 9-decenoate, can be readily hydrolyzed to the corresponding α,ω-unsaturated acids, such as 9-decenoic acid, which find utility in thermoset polymer applications, including thermoset urethanes. Alternatively, α,ω-unsaturated acids can be converted into α,ω-epoxy acids, which find utility, for example, in the manufacture of epoxy resins.
Cross-metathesis reactions have been disclosed, for example, in WO 96/04289, wherein methyl 9-octadecenoate is metathesized with ethylene in the presence of a ruthenium catalyst to form an α,ω-unsaturated acid or ester, namely, methyl 9-decenoate, and a co-product α-olefin, namely, 1-decene. Suitable catalysts for this cross-metathesis process comprise homogeneous ruthenium catalysts including first-generation Grubbs catalysts, exemplified by bis(tricyclohexylphosphine)-benzylidene ruthenium dichloride, and second-generation Grubbs catalysts, exemplified by tricyclohexylphosphine[1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene]ruthenium dichloride. “First-generation and second-generation Grubbs catalysts,” named for their principle inventor Robert H. Grubbs, are disclosed in the following illustrative patent publications: WO 96/04289 and WO 02/083742 and references therein. First-generation and second-generation Grubbs catalysts tend to be relatively tolerant towards air, moisture, and a wide array of polar functional groups, such as acid and ester functionalities. Moreover, in metathesis processes second-generation Grubbs catalysts exhibit high catalyst turnover numbers, provided that the reactants do not include ethylene. For the purposes of this invention, “catalyst turnover number” shall refer to the number of moles of α-functionalized internal olefin converted per mole of metathesis catalyst. A “high” catalyst turnover number shall mean a turnover number of greater than about 50,000 moles of α-functionalized internal olefin converted per mole of metathesis catalyst.
Disadvantageously, for cross-metathesis with ethylene, first- and second-generation Grubbs catalysts exhibit either rapid deactivation or unacceptable catalyst turnover numbers well below 50,000. The art suggests that, in part, this resultant catalyst instability is related to the presence of a metal-methylidene intermediate complex which forms on reaction of ethylene with the metal of the metathesis catalyst, typically, ruthenium. Consequently, the skilled artisan is confronted with a task of recovering the deactivated catalyst from the homogeneous reaction mixture, and then regenerating and recycling an activated catalyst back to the metathesis reaction. Unfortunately, recovery and regeneration of Grubbs catalysts are difficult to accomplish. Accordingly, the cross-metathesis of α-functionalized internal olefins with ethylene (ethenolysis) to higher valued cross-metathesis products, such as intermediate chain α,ω-functionalized olefins and co-product α-olefins, remains far from commercialization.
It would be desirable to discover a cross-metathesis process for preparing α,ω-functionalized olefins and co-product α-olefins from an α-functionalized internal olefin in which the metathesis catalyst possesses an insensitivity to polar functional groups, such as ester or carboxylic acid substituents, on the reactant olefin(s); in which the formation of any catalyst destabilizing intermediate complex is minimized, particularly with Grubbs catalysts; and in which the catalyst turnover number and catalyst lifetime are significantly improved as compared with prior art metathesis catalysts. With those advancements, the heretofore cost-prohibitive problem of recovering, regenerating and recycling a homogeneous metathesis catalyst should be avoided. Instead, with significantly improved catalyst turnover number and catalyst lifetime, economic studies indicate that a low concentration of catalyst can be employed, and the catalyst can be simply discarded upon its eventual deactivation.